The present invention relates to a heat treatment apparatus used in heat treatment of semiconductor devices, for example semiconductor wafers, and other devices which require heat treatment thereon.
FIG. 11 is a longitudinal sectional view of one portion of a typical heat treatment apparatus used in the manufacture of semiconductor devices, and oxidation, CVD and other processing for the heat treatment of semiconductor wafers. This heat treatment apparatus is provided with a heater chamber 1 which houses a process tube 4 which is the processing chamber which implements required processing such as heat treatment to the wafers 2 which are the objects for heat treatment, and beneath this process tube is provided a load lock chamber 8 via a manifold 6.
This manifold 6 is an empty space for coupling the process tube 4 and the load chamber 8. In addition, it is a shutout and standby space which separates the wafers 2 from the external air either prior to or after processing of the wafers 2 in the process tube 4.
The process tube 4 is a cylindrical body from a heat resistant material such as glass or the like which has one end sealed, and which does not exert any influence with respect to the object of heat treatment. A processing furnace in which a process tube such as this is housed vertically is called a vertical type furnace.
Around the periphery of this process tube 4 is a heater 10 for performing the necessary heat treatment with respect to the wafer 2. This heater 10 is connected to a heat control apparatus (not shown) so as to perform electrical heat control.
Moreover, the treatment temperature of the process tube 4 is set to 500.degree.-1000.degree. C. in the case of CVD processing, or to 800.degree.-1200.degree. C. with oxidation processing and dispersion processing.
In addition, to the manifold 6 provided to the lower end side of the process tube 4 is provided a gas introduction tube 12 for the introduction of the processing gas G.sub.1 into the process tube 4 in accordance with the processing of the object to be heat treated, and this gas introduction tube 12 is connected via a control valve and the like to a treatment gas source (not shown).
For example, the SiH.sub.4 used as the processing gas in CVD processing for the formation of a polysilicon film or the NH.sub.4 or SiH.sub.2 Cl.sub.2 gas used when there is the formation of a silicon nitride film, is introduced into the process tube 4 via the gas introduction tube 12. In addition, the treatment gas for purging the inside of the process tube 4 is N.sub.2 gas for example which is introduced from the gas introduction tube 12.
Inside this process tube 4 is provided a cylindrical partition wall 14 formed by glass or some other heat resistant material. The treatment gas G.sub.1 introduced from the gas introduction tube 12 drops from the top to the bottom from the side of the manifold 6 to the inner side of the cylindrical partition wall 14 and then rises on the outer side of the cylindrical partition wall 14 to return again to the manifold 6. More specifically, on the outer side portion of the cylindrical partition wall 14, the manifold 6 is connected to an exhaust pipe 16 which is the exhaust portion for exhausting the air in either the initial status (when there is start) or the treatment gas G.sub.1 which has recirculated, and this exhaust tube 16 is connected to a vacuum apparatus (not shown). More specifically, the treatment gas G.sub.1 and the air is forcedly exhausted via the vacuum apparatus to outside the process tube 4.
In addition, a wafer boat 18 rises and lowers so that wafers which are the item for treatment are loaded from the side of the load lock chamber 8 to the process tube 4. To an opening portion 19 on the side of the load lock chamber 8 of the manifold 6 is provided a shutter 20 which separates the load lock chamber 8.
This shutter 20 operates to seal the opening portion 19 of the manifold 6 when the wafer boat 18 is unloaded from the process tube 4.
The load lock chamber 8 is provided with a boat elevator 22 as the means of raising and lowering the wafer boat 18 to load and unload the wafer 2 to the process tube 4. To an upper surface of this boat elevator 22 is mounted a heat retention casing 24 to support the wafer boat 18 and form a thermally uniform region thereon. This heat retention casing 24 is formed with a flange 26 as the sealing lid for sealing the opening surface of the manifold 6 when there is the unloading of the wafers 2. More specifically, when there is unloading, the shutter 20 opens and the opening portion 19 is closed by the flange in the manifold 6 and is sealed from the load lock chamber 8.
Also, to the side of the load lock chamber 8 is provided a gate 28 for carrying the wafers 2 in and out prior to and after treatment, and this gate 28 is provided with a gate valve (not shown). The load lock chamber 8 has its side wall portions provided with a gas introduction tube 30 and a gas discharge tube 32.
The gas introduction tube 30 is connected to a gas source for a purge gas G.sub.2 which is an inert gas or the like, so that the load lock chamber 8 is filled with a non-oxidizing atmosphere (i.e. an atmosphere free of O.sub.2)
More specifically, the inside of the load lock chamber 8 is made a vacuum by exhausting through the gas discharge tube 32 and then the air or the gas G.sub.2 supplied through the gas discharge tube 32 is exhausted via the gas discharge tube 32.
However, in such a heat treatment apparatus, after the inside of the load lock chamber 8 has been made either a vacuum or is in a status of reduced pressure, it is necessary to purge the inert gas or the like but the flow of this purge gas G.sub.2 exerts an influence upon the wafer treatment speed.
More specifically, the load lock chamber 8 is provided with a boat elevator 22 as the means of transferring the wafers 2 which are to be treated, to the process tube 4, and the mechanism portion (ball screw) 34 of this boat elevator 22 generates dust due to mechanical friction therebetween and the wafers 2 must be protected from this dust. In addition, it is necessary that the purge gas G.sub.2 be uniformly applied to the wafers 2 and that there by no wafers portions not exposed to this gas as a result of eddies and the like. Furthermore, the load lock chamber 8 is provided with a boat elevator 22 and the like and so there is the tendency for the size of the entire heat treatment apparatus to increase. However, in order to respond to the requirement for a compact processing space, it is necessary to also reduce the area taken up by the mechanism for the supply of the purge gas.